Fluorescent lamps typically have a transparent glass envelope enclosing a sealed discharge space containing an inert gas and mercury vapor. When subjected to a current provided by electrodes, the mercury ionizes to produce radiation having primary wavelengths of 185 nm and 254 nm. This ultraviolet radiation, in turn, excites phosphors on the inside surface of the envelope to produce visible light which is emitted through the glass.
Generally, a fluorescent lamp for illumination uses a phosphor which absorbs the 254 nm Hg-resonance wave; the phosphor is activated so as to convert ultraviolet light into visible light. In order to improve the color-rendering properties and emission output of fluorescent lamps, efficient illumination of a white color has been recently provided using a three-band type fluorescent lamp which employs a mixture of red, green and blue-emitting phosphors. In such a three-band type phosphor lamp, the emitting colors of the respective phosphors are considerably different from one another. Therefore, if the emitting intensity of any of the three corresponding phosphors is decreased, color deviation occurs, degrading the color-rendering properties of the lamp. For example, LaPO4:Ce3+,Tb3+ (LAP) has been typically used as a green phosphor in combination with other phosphors (i.e., a red and blue phosphor). However, LAP is relatively expensive and can greatly increase the cost of the lamp.
Thus, a need exists for a phosphor blend that better matches the eye sensitivity curve, especially while avoiding the use of LAP in the lamp in order to reduce costs.